Significant effort has gone into the design of scalable micro-fluid ejection heads having staggered individual heater chips for use in wide-swath printing applications. In various wide-swath micro-fluid ejection heads designed to date, there is some amount of overlapping between two adjacent heater chips. The region in which two adjacent chips overlap is referred to as the “overlap region” or “stitching region.” Due to the overlapping of the two adjacent chips, there are two nozzles (one in each adjacent chip) that could be used in printing a particular raster line. Thus, two nozzle firing possibilities exist for each bit of print data on the overlapped region.
In prior systems, various methods have been used to determine which of the two aligned nozzles will fire in the overlapped region. One method involves disabling all of the overlapped nozzles in one chip and using all of the overlapped nozzles in the adjacent chip to print the stitching region portion of the data. Another method involves randomly selecting nozzles from both chips in the stitching region. One of the problems with these approaches is that temperature variations between adjacent staggered chips are not taken into account.
While printing, different chips in a multi-chip array will reach different temperatures based on the density of the image data in the portion of the image that each chip is responsible for printing. Variations in temperature between chips introduce variations in ink drop sizes. The heater chips that operate at higher temperatures eject larger drop sizes. Since page-wide micro-fluid ejection heads are constructed by staggering multiple heater chips, one would expect temperature variations between adjacent chips. Due to differences in ink drop sizes, an abrupt transition in temperature between adjacent chips could create visually detectable defects in the printed image in the overlapping region. To avoid visually detectable defects in the printed image, there should be a gradual and smooth transition from larger size ink drops (ejected from a higher temperature chip) to smaller size ink drops (ejected from a lower temperature chip).
What is needed, therefore, is a system for selecting nozzles within the overlapping region to provide a smooth transition in the printed image when there are temperature differences between adjacent heater chips.
In another aspect of the design of multi-chip wide-swath micro-fluid ejection heads, the overlapped nozzles in one chip should be perfectly aligned with the overlapped nozzles in an adjacent chip. However, this is generally not the case due to the various tolerances in chip placement and nozzle misdirection. Thus, a technique is needed to provide better blending to reduce visual defects caused by the misalignment between the two chips in the overlapping region. Ideally, the system for selecting nozzles within the overlapping region would account for chip-to-chip nozzle misalignments as well as chip-to-chip temperature differences.